A moisture-tolerant route to unprotected α/β-amino acid N-carboxyanhydrides and facile synthesis of hyperbranched polypeptides

Rigid, α-Helical Polypeptide Nanoprobes with Thermally Activated Delayed Fluorescence for Time-Resolved, High-Contrast Bioimaging

Thermally activated delayed fluorescence (TADF)-based nanoprobes are promising candidates as bioimaging agents, yet the fine-tuning of their photophysical properties through the modulation of the surrounding matrices remains largely unexplored. Herein, we report the development of polypeptide-TADF nanoprobes, where the rigid, α-helical polypeptide scaffold plays a critical role in enhancing the emission intensity and lifetime of the TADF fluorophore for bioimaging. The α-helical scaffolds not only spatially separated TADF molecules to avoid self-quenching but also anchored the dyes with minimized rotation and vibration. The nanoprobes thus exhibited >600 nm microsecond emission even in the presence of oxygen, facilitating cellular and animal imaging with a high signal-to-background ratio (SBR) by minimizing the interferences from autofluorescence signals. We believe that this work highlights the impact of the supporting polymeric conformation on the TADF performance, offering insights for the future design of time-resolved imaging probes.

Tuning Star Polymer Architecture to Tailor Secondary Structures and Mechanical Properties of Diblock Polypeptide Hydrogels for Direct Ink Writing

Hydrogel three-dimensional (3D) printing has emerged as a highly valuable fabrication tool for applications ranging from electronics and biomedicine. While conventional hydrogels such as gelatin, alginate, and hyaluronic acid satisfy biocompatibility requirements, they distinctly lack reproducibility in terms of mechanical properties and 3D printability. Aiming to offer a high-performance alternative, here we present a range of amphiphilic star-shaped diblock copolypeptides of l-glutamate and l-leucine residues with different topologies. Hydrophobic side chains of the l-leucine polymer block drive conformational self-assembly in water, spontaneously forming hydrogels with tunable mechanical properties, through variation of star topology. Their amenable shear-thinning and self-recovery properties render them suitable as hydrogel inks for direct ink writing. Well-defined 3D-printed structures can be readily generated and rapidly photo-cross-linked using visible light (405 nm) after methacrylamide functionalization, while hydrogel inks demonstrate good biocompatibility with top-seeded and encapsulated MC3T3 cells.

Hot shape transformation: the role of PSar dehydration in stomatocyte morphogenesis

Polysarcosine emerges as a promising alternative to polyethylene glycol (PEG) in biomedical applications, boasting advantages in biocompatibility and degradability. While the self-assembly behavior of block copolymers containing polysarcosine-containing polymers has been reported, their potential for shape transformation remains largely untapped, limiting their versatility across various applications. In this study, we present a comprehensive methodology for synthesizing, self-assembling, and transforming polysarcosine-poly(benzyl glutamate) block copolymers, resulting in the formation of bowl-shaped vesicles, disks, and stomatocytes. Under ambient conditions, the shape transformation is restricted to bowl-shaped vesicles due to the membrane's flexibility and permeability. However, dehydration of the polysarcosine broadens the possibilities for shape transformation. These novel structures exhibit asymmetry and possess the capability to encapsulate smaller structures, thereby broadening their potential applications in drug delivery and nanotechnology. Our findings shed light on the unique capabilities of polysarcosine-based polymers, paving the way for further exploration and harnessing of their distinctive properties in biomedical research.

The role of secondary structures of peptide polymers on antimicrobial efficacy and antibiotic potentiation

The rise of antibiotic resistance, biofilm formation, and dormant bacterial populations poses serious global health threats. Synthetic antimicrobial peptide (AMP) mimics offer promising alternatives, though the impact of secondary structures in polymeric AMP mimics on antimicrobial efficacy is underexplored. This study investigates chirality-controlled α-peptide polymers (D-PP and DL-PP), synthesized via ring-opening polymerization of allylglycine N-carboxy anhydrides and post-polymerization modification through thiol-ene click chemistry. D-PP adopts a stable helical structure under biomimetic conditions, whereas DL-PP remains random. This helical structure enhanced D-PP's antibacterial and antibiotic potentiation activities, amplifying antibiotic efficacy by 2- to 256-fold across various classes-including tetracyclines, ansamycins, fusidanes, macrolides, cephalosporins, and monobactams-against multidrug-resistant Gram-negative pathogens, while maintaining low hemolytic activity and high protease stability. Mechanistic investigations revealed that D-PP exhibited greater membrane interaction. D-PP and antibiotic combinations eradicated dormant bacterial populations and disrupted biofilms with minimal antimicrobial resistance development. This study paves the way for the rational design of polypeptide-based antimicrobial agents, harnessing chirality and secondary structural features to enhance the efficacy of synthetic antimicrobial peptide mimics.

Understanding Polyproline's Unusual Thermoresponsive Properties Using a Polyproline-Based Double Hydrophilic Block Copolymer

Polyproline is a unique thermoresponsive polymer characterized by large thermal and conformational hysteresis. This article employs polyproline-based double hydrophilic block copolymers (PNIPAMn-b-PLPm) to gain insight into polyproline's thermoresponsive mechanism. The amine-terminated poly(N-isopropylacrylamide) (NH2-PNIPAMm) was used as the macroinitiator for ring-opening polymerization of proline-NCA monomers, resulting in various block copolymers (PNIPAMn-b-PLPm) with varying PLP block lengths. Block copolymers' thermal phase transitions were compared with their homopolymer counterparts using turbidimetry, variable-temperature NMR, dynamic light scattering, and circular dichroism spectroscopy. These experiments revealed that regardless of their compositions, all block copolymers exhibited a two-stage collapse (TCP(PLP) > TCP(PNIPAM)) during the heating cycle. In contrast, only one clearing temperature (TCL) was observed during cooling. The observed clearing temperature is closely correlated to the clearing temperature of PNIPAM blocks, suggesting the role of water-soluble PNIPAM blocks in resolving the PLP blocks. Moreover, thermal and conformational hysteresis related to the polyproline block is significantly suppressed in the presence of a PNIPAM block. Linking PNIPAM blocks has two significant effects on PLP segments' thermoresponsive behavior. For example, during the heating cycle, the precollapsed PNIPAM chains (as TCP(PNIPAM) < TCP(PLP)) prevent orderly aggregation within the PLP block. Meanwhile, during the cooling cycle below the clearing temperature of the PNIPAM block, the PNIPAM chains impart water solubility (as TCL(PNIPAM) > TCL(PLP)) to the collapsed PLP chains. Overall, the PNIPAM block imparts water solubility and perturbs PLP chains to form the native aggregate structure, suppressing the hysteresis effect. Accordingly, the large thermal and conformational hysteresis associated with native PLP chains appears to result from a noninterfering aggregation above the critical temperature.

Catalyst-free ring opening of azlactones in water microdroplets

A catalyst-free method was developed for the ring opening of azlactones (also known as oxazolones) in water microdroplets. Azlactone was dissolved in a water : acetonitrile (1 : 1) mixture, and the solution is sprayed by using nitrogen gas at a pressure of 120 psi to generate microdroplets. This method promoted selective cleavage of the lactone bond to afford the corresponding N-benzoyl derivatives in up to 94% isolated yield with no epimerization. Our method produces the ring-opening products in milliseconds (up to 94 μmol for 33.3 minutes), and may have utility for high-throughput synthesis applications.

Diradicaloid-Loaded Polypeptide Nanoparticles for Two-Photon NIR Phototheranostics

Stable organic radicals, with unique electronic transitions from the ground state (D0) to the doublet excited state (D1), show promise as high-fluorescence quantum yield dyes. While organic small-molecule photosensitizers (PSs) have advanced for tumor photodynamic therapy (PDT), opportunities exist to enhance their performance and functionality. Herein, we synthesized Thiele's fluorocarbon derivative diradicaloid TFC-I with nearly 100% PLQY and integrated it into amphiphilic polypeptide nanoparticles, P-TI, using a precursor-doping approach. P-TI demonstrated notable features including high photostability, aggregation-induced emission, bright near-infrared fluorescence, substantial quantum yield (37% PLQY), robust near-infrared two-photon absorption (∼400 GM cross section), and superior ROS generation compared to commercial PSs. In vitro and in vivo experiments confirmed that P-TI performed well in mitochondria-targeted PDT, two-photon fluorescence imaging, and biosafety. This work highlights the use of organic stable radicals with precursor-doping for efficient PDT and deep tumor tissue imaging.

Recyclable Polythioesters and Poly(thioester-co-peptoid)s via Ring-Opening Cascade Polymerization of Amino Acid N-Carboxyanhydrides

Polythioesters (PTEs) are emerging sustainable polymers for their degradability and recyclability. However, low polymerizability of monomers and extensive side reactions often hampered the polymerization process. Moreover, copolymers containing both thioester and other types of functional groups in the backbone are highly desirable but rarely accomplished owing to several synthetic challenges. Here, we report the ring-opening cascade polymerization (ROCAP) of N-(2-(acetylthio)ethyl)-glycine N-carboxyanhydrides (TE-NCA) to afford recyclable PTEs and unprecedented poly(thioester-co-peptoid)s (P(TE-co-PP)s) in a controlled manner. By developing appropriated carboxylic acid-tertiary amine dual catalysts, intramolecular S-to-N acyl shift is coupled into the ROCAP process of TE-NCA to yield products with dispersity below 1.10, molecular weight (Mn) up to 84.5 kDa, and precisely controlled ratio of thioester to peptoids. Random copolymerization of sarcosine NCA (Sar-NCA) and TE-NCA gives thioester-embedded polysarcosine with facile backbone degradation while maintaining the water solubility. This work represents a paradigm shift for the ROP of NCAs, enriches the realm of cascade polymerizations, and provides a powerful synthetic approach to functional PTEs and P(TE-co-PP)s that are otherwise difficult or impossible to make.

Photochemical Deracemization of N-Carboxyanhydrides En Route to Chiral α-Amino Acid Derivatives

Readily accessible, racemic N-carboxyanhydrides (NCAs) of α-amino acids underwent a deracemization reaction upon irradiation at λ=366 nm in the presence of a chiral benzophenone catalyst. The enantioenriched NCAs (up to 98 % ee) serve as activated α-amino acid surrogates and, due to their instability, they were directly converted into consecutive products. N-Protected α-amino acid esters were obtained after reaction with MeOH and N-benzoylation (14 examples, 70 %-quant., 82-96 % ee). Other consecutive reactions included amide (ten examples, 65 %-quant., 90-98 % ee) and peptide (three examples, 75-89 %, d. r.=97/3 to 94/6) bond formation. Limitations of the method relate for some NCAs to issues with solubility, photooxidation, and high configurational lability.

Self-promoted Controlled Ring-opening Polymerization via Side Chain-mediated Proton Transfer for the Synthesis of Tertiary Amine-pendant Polypeptoids

Proton transfer is essential in virtually all biochemical processes, with enzymes facilitating this transfer by optimizing the proximity and orientation of reactants through site-specific hydrogen bonds. Proton transfer is also crucial in the rate-determining step for the ring-opening polymerization of N-carboxyanhydrides (NCAs), widely used to prepare various peptidomimetic materials. This study utilizes side chain-assisted strategy to accelerate the rate of chain propagation by using NCAs with tertiary amine pendants. This moiety enables hydrogen bond formation between the incoming NCA and the polymer amino growing end. The tertiary amine side chain of the NCA forms a proton shuttle, via a less constrained transition state, to facilitate the proton transfer process. Moreover, the tertiary amine side chains enable the precipitation of NCA monomers through in situ protonation during the monomer synthesis. This greatly facilitates the synthesis of these unreported monomers, allowing the direct controlled synthesis of tertiary amine-pendant polypeptoids. This side chain-promoted polymerization has rarely been reported. Additionally, the tertiary amine side chains, as widely used functional groups, endow the polymers with unique properties including pH- and thermo-responsiveness, tunable pKas, and siRNA transfection capability. The self-promoted synthesis, facile monomer preparation, and attractive properties make tertiary amine-pendant polypeptoids promising materials for various applications.

Open-vessel polymerization of N-carboxyanhydride (NCA) for polypeptide synthesis

Synthetic polypeptides, also known as poly(α-amino acids), have the same polyamide backbone structures as natural proteins and peptides. As an important class of biomaterials, polypeptides have been widely used because of their biocompatibility, bioactivity and biodegradability. Ring-opening polymerization of N-carboxyanhydride (NCA) is a classical and widely used method for the synthesis of polypeptides. The dominantly used primary amine-initiated NCA polymerization can yield well-defined polymers and complex macromolecular architectures, but the reaction is slow and sensitive to moisture, making it necessary to use anhydrous solvents and a glovebox. One solution is to use lithium hexamethyldisilazide (LiHMDS) as the initiator, as described in this protocol. LiHMDS-initiated NCA polymerization is less sensitive to moisture and can be carried out in an open vessel outside the glovebox. It is also very fast; the reaction can be complete within 5 min to produce 30-mer polypeptides. In this protocol, poly(γ-benzyl-L-glutamate) is prepared as an example, but the protocol can easily be adapted to the synthesis of other polypeptides by generating NCAs from different amino acids, making it particularly suitable for the efficient parallel synthesis of polypeptide libraries. We provide detailed procedures for NCA synthesis and purification, the method of polymer end-group modification and measurement of polymerization kinetics and reactivity ratio. The procedure for synthesis of monomers and polymerization to form polypeptides requires <1 d. The superfast and open-vessel NCA polymerization method described here will probably enable a wide range of applications in the synthesis and functional study of polypeptide biomaterials.

Facile Preparation of Heteropolypeptides from Crude Mixtures of α-Amino Acid N-Carboxyanhydrides

Heteropolypeptides bearing two or more functional side chains are promising polymeric materials for various biomedical applications. However, conventional preparation of heteropolypeptides relies on the synthesis and purification of each N-carboxyanhydride (NCA) monomer in a separate manner, which substantially increases the time and cost. Herein, we report the facile preparation of heteropolypeptides with up to 86% yield within several hours, which are obtained from a mixture of crude NCA monomers. The combination of n-hexane precipitation and biphasic segregation effectively removed >90% impurities from crude NCA mixtures, allowing for the successful polymerization process. Various heteropolypeptides with monomodal distribution and narrow dispersity were efficiently prepared, whose compositions were predetermined by the feeding ratios of amino acids. We believe that this work significantly simplifies the preparation of various heteropolypeptides, boosting the downstream studies of these promising materials.

Recent Advances and Future Developments in the Preparation of Polypeptides via N-Carboxyanhydride (NCA) Ring-Opening Polymerization

Polypeptides have the same or similar backbone structures as proteins and peptides, rendering them as suitable and important biomaterials. Amino acid N-carboxyanhydrides (NCA) ring-opening polymerization has been the most efficient strategy for polypeptide preparation, with continuous advance in the design of initiators, catalysts and reaction conditions. This Perspective first summarizes the recent progress of NCA synthesis and purification. Subsequently, we focus on various initiators for NCA polymerization, catalysts for accelerating polymerization or enhancing the controllability of polymerization, and recent advances in the reaction approach of NCA polymerization. Finally, we discuss future research directions and open challenges.

Facile Preparation of Polysarcosine-Tethered Inorganic Nanospheres by Using Unimolecular Polypept(o)ides as Template

Polymer-inorganic nanocomposites that integrate the advantages of both polymers and inorganic nanoparticles (NPs) are broadly exploited for versatile applications. Especially, emerging polymer-templated preparation of inorganic NPs has drawn extensive attention, which is ascribed to simplified synthesis and feasible tunability. However, how to precisely fabricate biocompatible polymer-inorganic NPs remains unsolved. In this article, by mild ring opening polymerization (ROP) of β-benzyl L-aspartate N-carboxyanhydrides (BLA-NCAs) and sarcosine N-carboxyanhydrides (Sar-NCAs) and subsequent debenzylation, a series of poly(amino acid)-based unimolecular micelles (PAMAM-g-(PLA-b-PSar)) are facilely synthesized. Afterward, by utilization of these star-like polymers as template, the controllable preparation of various PSar-tethered inorganic NPs is investigated and characterized meticulously. This general strategy for the preparation of PSar-tethered inorganic NPs can bring a great chance for future fabrication of biomedical nanoplatforms.

Nonionic Water-Soluble Oligo(ethylene glycol)-Modified Polypeptides with a β-Sheet Conformation

The secondary structures of polypeptides, such as an α-helix and a β-sheet, often impart specific properties and functions, making the regulation of their secondary structures of great significance. Particularly, water-soluble polypeptides bearing a β-sheet conformation are rare and challenging to achieve. Here, a series of oligo(ethylene glycol)-modified lysine N-carboxylic anhydrides (EGmK-NCA, where m = 1-3) and the corresponding polymers EGmKn are synthesized, with urethane bonds as the linker between the side-chain EG and lysine. The secondary structure of EGmKn is delicately regulated by both m and n, the length (number of repeating units) of EG and the degree of polymerization (DP), respectively. Among them, EG2Kn adopts a β-sheet conformation with good water solubility at an appropriate DP and forms physically cross-linked hydrogels at a concentration as low as 1 wt %. The secondary structures of EG1Kn can be tuned by DP, exhibiting either a β-sheet or an α-helix, whereas EG3Kn appears to a adopt pure and stable α-helix with no dependence on DP. Compared to previous works reporting EG-modified lysine-derived polypeptides bearing exclusively an α-helix conformation, this work highlights the important and unexpected role of the urethane connecting unit and provides useful case studies for understanding the secondary structure of polypeptides.

Effects of chain lengths and backbone chirality on the bone-targeting ability of poly(glutamic acid)s

Anionic synthetic polypeptides are promising candidates as standalone bone-targeting drug carriers. Nevertheless, the structure-property relationship of the bone-targeting ability of polypeptides remains largely unexplored. Herein we report the optimization of the in vitro and in vivo bone-targeting ability of poly(glutamic acid)s (PGAs) by altering their chain lengths and backbone chirality. PGA 100-mers exhibited higher hydroxyapatite affinity in vitro, but their rapid macrophage clearance limited their targeting ability. Shorter PGA was therefore favored in terms of in vivo bone targeting. Meanwhile, the backbone chirality showed less significant impact on the in vitro and in vivo targeting behavior. This study highlights the modulation of structural parameters on the bone-targeting performance of anionic polypeptides, shedding light on the future design of polypeptide-based carriers.

Aromatic poly (amino acids) as an effective low-temperature demulsifier for treating crude oil-in-water emulsions

Amphiphilic aromatic poly (amino acids) polymers were designed as biodegradability demulsifiers with higher aromaticity, stronger polarity, and side chain-like combs. The effects of demulsifier dosage, structural characteristics and emulsion properties such as pH, salinity, and oil content on the demulsification efficiency were investigated. The results show that the poly (L-glutamic-benzyl ester)-block-poly (L-phenylalanine) (PBLG15-b-PPA15) as the demulsifier can remove more than 99.97% of the oil in a 5.0 wt% oil-in-water (O/W) emulsion at room temperature within 2 min. The poly (L-tyrosine)-block-poly (L-phenylalanine) (PTyr15-b-PPA15) with environmental durability demonstrates high effectiveness, universality, and demulsification speed. It achieves a remarkable demulsification efficiency of up to 99.99% for a 20.0 wt% O/W emulsion at room temperature. The demulsification mechanism indicates that demulsifiers have sufficient interfacial activity can quickly migrate to the oil-water interface after being added to the emulsions. Additionally, when demulsifiers are present in a continuous phase in the molecular form, their "teeth" side chains are beneficial for increasing coalescence and flocculation capacities. Furthermore, according to the Density Functional Theory (DFT) calculations, enhancing the intermolecular interactions between demulsifiers and the primary native surfactants that form an oil-water interfacial film is a more efficient approach to reducing demulsification temperature and improving demulsification efficiency and rate.

Self-assembled branched polypeptides as amelogenin mimics for enamel repair

The regeneration of demineralized enamel holds great significance in the treatment of dental caries. Amelogenin (Ame), an essential protein for mediating natural enamel growth, is no longer secreted after enamel has fully matured in childhood. Although biomimetic mineralization based on peptides or proteins has made significant progress, easily accessible, low-cost, biocompatible and highly effective Ame mimics are still lacking. Herein, we construct a series of amphiphilic branched polypeptides (CAMPs) by facile coupling of the Ame's C-terminal segment and poly(γ-benzyl-L-glutamate), which serves to simulate the Ame's hydrophobic N-terminal segment. Among them, CAMP15 is the best biomimetic mineralization template with great self-assembly performance to guide the oriented crystallization of hydroxyapatite and is capable of inhibiting the adhesion of Streptococcus mutans and Staphylococcus aureus on the enamel surfaces. This work highlights the potential application of amphiphilic branched polypeptide as Ame mimics in repairing defected enamel, providing a promising strategy for prevention and treatment of dental caries.

Polypeptide- and Protein-Based Conjugate Nanoparticles via Aqueous Ring-Opening Polymerization-Induced Self-Assembly (ROPISA)

Protein-polymer conjugates and polymeric nanomaterials hold great promise in many applications including biomaterials, medicine, or nanoelectronics. In this work, the first polymerization-induced self-assembly (PISA) approach performed in aqueous medium enabling protein-polymer conjugates and nanoparticles entirely composed of amino acids is presented by using ring-opening polymerization (ROP). It is indeed shown that aqueous ring-opening polymerization-induced self-assembly (ROPISA) can be used with protein or peptidic macroinitiators without prior chemical modification and afford the simple preparation of nanomaterials with protein-like property, for example, to implement biomimetic thermoresponsivity in drug delivery.

Efficient Catalyst-Free One-Pot Synthesis of Polysaccharide-Polypeptide Hydrogels in Aqueous Solution

The preparation of polysaccharide-peptide hydrogels usually involves multiple synthetic steps, thus reducing the effectiveness and practicality of these approaches. Inspired by recent discoveries in aqueous N-carboxyanhydride (NCA) ring-opening polymerization (ROP) and ring-opening polymerization-induced nanogelation, we present an aqueous one-pot strategy to prepare polysaccharide-polypeptide hydrogels. In this study, water-soluble polysaccharide carboxymethyl chitosan is used as the macromolecular initiator to prepare polysaccharide-polypeptide copolymers through the aqueous ROP of NCA. The catalyst-free approach afforded hydrogels with properties that could be controlled by adjusting the type and amount of NCA used, with the elastic modulus ranging from 50 Pa to 18000 Pa. The hydrogen bond-cross-linked hydrogel exhibited self-healing and injectable properties. Morphology characterization revealed that micelles were formed in the early stage of reaction, suggesting that the polymerization follows an aqueous ring-opening polymerization-induced self-assembly (ROPISA) mechanism and that aggregation of micelles during the reaction caused the gelation. Moreover, the hydrogels displayed high swelling ratios (>95% water content), and hemolysis and cytotoxicity experiments demonstrated that the hydrogels had excellent biocompatibility, indicating their potential in medical applications.

Nanoassemblies of heptamethine cyanine dye-initiated poly(amino acid) enhance ROS generation for effective antitumour phototherapy

Phototherapy shows great potential for pinpoint tumour treatment. Heptamethine cyanine dyes like IR783 have high potential as agents for antitumour phototherapy due to their inherent tumour targeting ability, though their effectiveness in vivo is unsatisfactory for clinical translation. To overcome this limitation, we present an innovative strategy involving IR783-based polymeric nanoassemblies that improve the dye's performance as an antitumoural photosensitizer. In the formulation, IR783 is modified with cysteamine and used to initiate the ring-opening polymerization (ROP) of the N-carboxyanhydride of benzyl-L-aspartate (BLA), resulting in IR783-installed poly(BLA). Compared to free IR783, the IR783 dye in the polymer adopts a twisted molecular conformation and tuned electron orbital distribution, remarkably enhancing its optical properties. In aqueous environments, the polymers spontaneously assemble into nanostructures with 60 nm diameter, showcasing surface-exposed IR783 dyes that function as ligands for cancer cell and mitochondria targeting. Moreover, the nanoassemblies stabilized the dyes and enhanced the generation of reactive oxygen species (ROS) upon laser irradiation. Thus, in murine tumor models, a single injection of the nanoassemblies with laser irradiation significantly inhibits tumour growth with no detectable off-target toxicity. These findings highlight the potential for improving the performance of heptamethine cyanine dyes in antitumor phototherapy through nano-enabled strategies.

Synthetic Polypeptide Bioadhesive Based on Cation-π Interaction and Secondary Structure

Bioadhesives have garnered widespread attention in the biomedical field, for wound healing and tissue sealing. However, challenges exist due to the inferior performance of bioadhesives, including weak adhesion, poor biocompatibility, or lack of biodegradability. In this work, we demonstrate the fabrication of hydrogel adhesive based on polypeptides composed of lysine and glutamic acid. The cation-π interaction between the ammonium cations and phenyl groups endows the hydrogel with strong cohesion, and the hydrophobicity of the phenyl group significantly enhances the interaction between polypeptides and the substrate interface, leading to excellent adhesive performance. The equivalent molar ratio of ammonium cations and the phenyl group is beneficial for the enhancement of adhesiveness. Furthermore, we discover that the polypeptides with an α-helix exhibit better adhesiveness than the polypeptides with a β-sheet because the α-helical structure can increase the exposure of the side group on the polypeptide surface, which further strengthens the interaction between polypeptides and the substrate. Besides, this synthetic polypeptide adhesive can seal the tissue quickly and remain intact in water. This adhesive holds significant promise for application in wound healing and tissue sealing, and this study provides insight into the development of more peptide-based adhesives.

Facile Synthesis of High Molecular Weight Poly(ethylene glycol)-b-poly(amino acid)s by Relay Polymerization

Poly(amino acid)s (PAAs) are one kind of favorable biopolymer that can be used as a drug or gene carrier. However, conventional ring-opening polymerization of PAAs is slow and needs a strict anhydrous environment with an anhydrous reagent as well as the product without enough high molecular weight (Mn), which limits the expanding of PAAs' application. Herein, we took BLG-NCA as the monomer to quickly synthesize one kind of high Mn amphiphilic copolymer, poly(ethylene glycol)-b-poly(γ-benzyl-l-glutamic acid) (PEG-PBLG), by relay polymerization with a simple one-pot method within 3 h in mild conditions (open air, moisture insensitive). In the polymerization process, ring-opening polymerization-induced self-assembly in sodium bicarbonate aqueous solution first occurred to obtain low Mn PEG-PBLG seeds without purification. Then γ-benzyl-l-glutamate N-carboxyanhydride (BLG-NCA) dichloromethane solution was added into PEG-PBLG seeds directly and stirred vigorously to form am emulsion; during this process, the amphiphilic PEG-PBLG seeds will anchor on the interface of DCM and water to ensure the concentration of α-helix rigid PBLG in DCM to maintain the following relay polymerization. Then, high Mn PEG-PBLG was obtained in mild conditions in one pot. We found that the α-helix rigid structure was essential for relay polymerization by studying the synthetic speed of amphiphilic copolymer with different secondary structures. MOE simulation results showed that PBLG and BLG-NCA tended to form a double hydrogen bond, which was beneficial to relay polymerization because of higher local concentrations that can produce more double hydrogen bonds. Our strategy can quickly obtain high Mn PEG-PBLG (224.9 KDa) within 3 h from PEG-NH2 and BLG-NCA in one pot and did not need an extra initiator. After deprotection, the poly(ethylene glycol)-b-poly(l-glutamate acid) (PEG-PGA) with high Mn as a second product can be used as an excellent antitumor drug carrier. The high Mn PEG-PGA can achieve an encapsulation rate of 86.7% and a drug loading rate of 47.3%, which is twice that of the low Mn PEG-PGA. As a result, the synthesis of PEG-PBLG by relay polymerization simplified the process of PEG-PAA polymerization and increased the Mn. In addition, this method opened a way to obtain other kinds of high Mn PEG-PBLG values in the future.

Glycine N-Thiocarboxyanhydride: A Key to Glycine-Rich Protein Mimics

Glycine-rich proteins (GRPs) containing a high content of glycine residues (>30%) possess unique structural stability. However, the controllable synthesis of glycine-rich poly(amino acid)s (PAAs) to mimic GRPs has not been realized yet due to the poor solubility of polyglycine segments. We developed a novel method to synthesize glycine-rich PAAs via the controlled ring-opening copolymerization of glycine-N-thiocarboxyanhydrides (Gly-NTA) with sarcosine-N-carboxyanhydride and ε-Cbz-l-lysine-N-carboxyanhydride. The random copolymerization is evidenced by a kinetic study that shows that the propagation rate constant of Gly-NTA is close to those of comonomers. The copolymers exhibit predictable molecular weights between 4.5 and 24.6 kg/mol and tunable glycine incorporation, varying from 10.3 to 59.2%. Poly(Gly-r-Sar) samples with various glycine contents form nanoparticles or a hydrogel in water. Remarkably, the β-sheet folding of poly(Gly-r-Lys) remains intact in a neutral environment where the amine groups are protonated. Overall, the strategy paves the way to engineer glycine-rich PAAs and thereby expands their applications.

Paclitaxel prodrug-encapsulated polypeptide micelles with redox/pH dual responsiveness for cancer chemotherapy

Polypeptides are a highly promising carrier for delivering hydrophobic drugs, due to their excellent biocompatibility, non-toxicity, and non-immunogenicity. Herein, a redox and pH dual-responsive poly(ethylene glycol)-SS-b-polypeptide micelles encapsulated with disulfide bridged paclitaxel-pentadecanoic acid prodrug was developed for cancer chemotherapy. First of all, disulfide bridged paclitaxel-pentadecanoic acid prodrug (PTX-SS-COOH) and poly(ethylene glycol)-SS-b-polylysine-b-polyphenylalanine (mPEG-SS-b-PLys-b-PPhe, ESLP) were synthesized and confirmed via NMR, MS, FT-IR or GPC. After that, PTX-SS-COOH (PSH) embedded mPEG-SS-b-PLys-b-PPhe (ESLP/PSH) micelles were prepared by mixing method based on electrostatic interactions and hydrophobic forces. For comparison, mPEG-b-PLys-b-PPhe (ELP) was mixed with PTX-SS-COOH to generate another kind of micelles (ELP/PSH). The characterization of ESLP/PSH micelles through dynamic light scattering (DLS) and transmission electron microscopy (TEM) revealed a spherical structure with a diameter of approximately 170 nm. It is noteworthy that ESLP/PSH micelles displayed a high drug-loading rate of 22.84%, and excellent stability, which can be attributed to the specific interactions between the prodrug and copolymer. Drug release analysis demonstrated that the micelles exhibited a substantial release of PTX in the presence of GSH at pH 5.0, indicating a pH and redox dual responsiveness. In vivo pharmacokinetic study revealed the ESLP/PSH micelles had increased bioavailability and an extended circulation time. Ultimately, antitumor efficacy and systemic toxicity evaluation in 4 T1 tumor-bearing mice confirmed that ESLP/PSH micelles achieved the highest level of tumor growth inhibition (ca. 83%) and the lowest systemic toxicity in comparison with ELP/PSH micelles and commercialized Taxol®. Taken together, the dual responsive micelles represent a promising PTX formulation with potential clinical application in cancer chemotherapy.

Competition between β-Sheet and Coacervate Domains Yields Diverse Morphologies in Mixtures of Oppositely Charged Homochiral Polypeptides

Biomolecular assembly processes involving competition between specific intermolecular interactions and thermodynamic phase instability have been implicated in a number of pathological states and technological applications of biomaterials. As a model for such processes, aqueous mixtures of oppositely charged homochiral polypeptides such as poly-l-lysine and poly-l-glutamic acid have been reported to form either β-sheet-rich solid-like precipitates or liquid-like coacervate droplets depending on competing hydrogen bonding interactions. Herein, we report studies of polypeptide mixtures that reveal unexpectedly diverse morphologies ranging from partially coalescing and aggregated droplets to bulk precipitates, as well as a previously unreported re-entrant liquid-liquid phase separation at high polypeptide concentration and ionic strength. Combining our experimental results with all-atom molecular dynamics simulations of folded polypeptide complexes reveals a concentration dependence of β-sheet-rich secondary structure, whose relative composition correlates with the observed macroscale morphologies of the mixtures. These results elucidate a crucial balance of interactions that are important for controlling morphology during coacervation in these and potentially similar biologically relevant systems.

Biodegradable Polymers and Polymer Composites with Antibacterial Properties

Antibiotic resistance is one of the greatest threats to global health and food security today. It becomes increasingly difficult to treat infectious disorders because antibiotics, even the newest ones, are becoming less and less effective. One of the ways taken in the Global Plan of Action announced at the World Health Assembly in May 2015 is to ensure the prevention and treatment of infectious diseases. In order to do so, attempts are made to develop new antimicrobial therapeutics, including biomaterials with antibacterial activity, such as polycationic polymers, polypeptides, and polymeric systems, to provide non-antibiotic therapeutic agents, such as selected biologically active nanoparticles and chemical compounds. Another key issue is preventing food from contamination by developing antibacterial packaging materials, particularly based on degradable polymers and biocomposites. This review, in a cross-sectional way, describes the most significant research activities conducted in recent years in the field of the development of polymeric materials and polymer composites with antibacterial properties. We particularly focus on natural polymers, i.e., polysaccharides and polypeptides, which present a mechanism for combating many highly pathogenic microorganisms. We also attempt to use this knowledge to obtain synthetic polymers with similar antibacterial activity.

Ring-Opening Polymerization of Amino Acid N-Carboxyanhydrides with Unprotected/Reactive Side Groups. I. d-Penicillamine N-Carboxyanhydride

The ring-opening (co)polymerization (ROP) of N-carboxyanhydride (NCA) monomers bearing unprotected/reactive side groups is rare and challenging. Here, we report the ROP of a d-penicillamine NCA (Pen-NCA) monomer for the synthesis of tertiary thiol-functionalized (co)polypeptides. Through judicious selection of reaction solvents and the use of benzoic acid as an additive in the ROP, the intramolecular isomerization side reactions of Pen-NCA are suppressed, generating homo- and copolypeptides with improved yield, high molecular weight, and narrow molecular weight distributions. Successful postpolymerization modifications of the d-Pen-containing copolypeptides on the tertiary thiols are achieved with high efficiency through thiol-Michael, S_N2, and nitrosylation reactions. This work provides an efficient protection-free approach to generating functional polypeptides and creates a fundamental understanding for Pen-NCA chemistry.

Advance in the Polymerization Strategy for the Synthesis of β-Peptides and β-Peptoids

Peptide mimics, possessing excellent biocompatibility and protease stability, have attracted broad attention and research in the biomedical field. β-Peptides and β-peptoids, as two types of vital peptide mimics, have demonstrated great potential in the field of foldamers, antimicrobials and protein binding, etc. Currently, the main synthetic strategies for β-peptides and β-peptoids include solid-phase synthesis and polymerization. Among them, polymerization in one-pot can minimize the repeated separation and purification used in solid-phase synthesis, and has the advantages of high efficiency and low cost, and can synthesize β-peptides and β-peptoids with high molecular weight. This review summarizes the polymerization methods for β-peptides and β-peptoids. Moreover, future developments of the polymerization method for the synthesis of β-peptides and β-peptoids will be discussed.

Tailored Polypeptide Star Copolymers for 3D Printing of Bacterial Composites Via Direct Ink Writing

Hydrogels hold much promise for 3D printing of functional living materials; however, challenges remain in tailoring mechanical robustness as well as biological performance. In addressing this challenge, the modular synthesis of functional hydrogels from 3-arm diblock copolypeptide stars composed of an inner poly(l-glutamate) domain and outer poly(l-tyrosine) or poly(l-valine) blocks is described. Physical crosslinking due to ß-sheet assembly of these star block copolymers gives mechanical stability during extrusion printing and the selective incorporation of methacrylate units allows for subsequent photocrosslinking to occur under biocompatible conditions. This permits direct ink writing (DIW) printing of bacteria-based mixtures leading to 3D objects with high fidelity and excellent bacterial viability. The tunable stiffness of different copolypeptide networks enables control over proliferation and colony formation for embedded Escherichia coli bacteria as demonstrated via isopropyl ß-d-1-thiogalactopyranoside (IPTG) induction of green fluorescent protein (GFP) expression. This translation of molecular structure to network properties highlights the versatility of these polypeptide hydrogel systems with the combination of writable structures and biological activity illustrating the future potential of these 3D-printed biocomposites.

An immunomodulatory polypeptide hydrogel for osteochondral defect repair

Osteochondral injury is a common and frequent orthopedic disease that can lead to more serious degenerative joint disease. Tissue engineering is a promising modality for osteochondral repair, but the implanted scaffolds are often immunogenic and can induce unwanted foreign body reaction (FBR). Here, we prepare a polypept(o)ide-based PAA-RGD hydrogel using a novel thiol/thioester dual-functionalized hyperbranched polypeptide P(EG₃Glu-co-Cys) and maleimide-functionalized polysarcosine under biologically benign conditions. The PAA-RGD hydrogel shows suitable biodegradability, excellent biocompatibility, and low immunogenicity, which together lead to optimal performance for osteochondral repair in New Zealand white rabbits even at the early stage of implantation. Further in vitro and in vivo mechanistic studies corroborate the immunomodulatory role of the PAA-RGD hydrogel, which induces minimum FBR responses and a high level of polarization of macrophages into the immunosuppressive M2 subtypes. These findings demonstrate the promising potential of the PAA-RGD hydrogel for osteochondral regeneration and highlight the importance of immunomodulation. The results may inspire the development of PAA-based materials for not only osteochondral defect repair but also various other tissue engineering and bio-implantation applications.

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A polypept(o)ide-based hydrogel.

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Prominent and early osteochondral repair.

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Minimized immunogenicity.

Photo-On-Demand Synthesis of α-Amino Acid N-Carboxyanhydrides with Chloroform

Amino acid N-carboxyanhydrides (NCAs) are conventionally synthesized from α-amino acids and phosgene. The present study reports in situ photo-on-demand phosgenation reactions of amino acids with CHCl₃ for synthesizing NCAs. A series of NCAs were obtained on a gram scale upon photo-irradiation of a mixture solution of CHCl₃ and CH₃CN containing an amino acid at 60-70 °C under O₂ bubbling. This method presents a safe and convenient reaction controlled by light without special apparatuses and reagents.

Recent advances in post-polymerization modifications on polypeptides: synthesis and applications

Polypeptides, a kind of very promising biomaterial, have shown a wide range of applications due to their excellent biocompatibility, easy accessibility, and structural variability. To synthesize polypeptides with desired functions, post-polymerization modification (PPM) plays an important role in introducing novel chemical structure on their side-chains. The key of PPM strategy is to develop highly selective and efficient reactions that can couple the additional functional moieties with pre-installed side-chain functionalities on polypeptides. In this minireview, classic PPM reactions and especially their recent progresses are summarized, including different modification approaches for unsaturated alkyl group, oxygen-containing functional group, nitrogen-containing functional group, sulfur-containing functional group and other special functional group on side chains. In addition, this review also highlights the applications of structure-diversified polypeptides generated via PPM strategy in the field of biomaterial.

Water-Assisted and Protein-Initiated Fast and Controlled Ring-Opening Polymerization of Proline N-Carboxyanhydride

The production of polypeptides via the ring-opening polymerization (ROP) of N-carboxyanhydride (NCA) is usually conducted under stringent anhydrous conditions. The ROP of proline NCA (ProNCA) for the synthesis of poly-_L-proline (PLP) is particularly challenging due to the premature product precipitation as polyproline type I helices, leading to slow reactions for up to one week, poor control of the molar mass and laborious workup. Here, we report the unexpected water-assisted controlled ROP of ProNCA, which affords well-defined PLP as polyproline II helices in 2–5 minutes and almost-quantitative yields. Experimental and theoretical studies together suggest the as-yet-unreported role of water in facilitating proton shift, which significantly lowers the energy barrier of the chain propagation. The scope of initiators can be expanded from hydrophobic amines to encompass hydrophilic amines and thiol-bearing nucleophiles, including complex biomacromolecules such as proteins. Protein-mediated ROP of ProNCA conveniently affords various protein-PLP conjugates via a grafting-from approach. PLP modification not only preserves the biological activities of the native proteins, but also enhances their resistance to extreme conditions. Moreover, PLP modification extends the elimination half-life of asparaginase (ASNase) 18-fold and mitigates the immunogenicity of wt ASNase >250-fold (ASNase is a first-line anticancer drug for lymphoma treatment). This work provides a simple solution to a long-standing problem in PLP synthesis, and offers valuable guidance for the development of water-resistant ROP of other proline-like NCAs. The facile access to PLP can greatly boost the application potential of PLP-based functional materials for engineering industry enzymes and therapeutic proteins.

Biomimetic Glycosylated Polythreonines by N-Carboxyanhydride Polymerization

Glycosylated threonine (Thr) is a structural motif found in seemingly disparate natural proteins from deep-sea collagen to mucins. Synthetic mimics of these important proteins are of great interest in biomedicine. Such materials also provide ready access to probe the contributions of individual amino acids to protein structure in a controlled and tunable manner. N-Carboxyanhydride (NCA) polymerization is one major route to such biomimetic polypeptides. However, challenges in the preparation and polymerization of Thr NCAs have impeded obtaining such structures. Here, we present optimized routes to several glycosylated and acetylated Thr NCAs of high analytical purity. Transition metal catalysis produced tunable homo-, statistical, and block-polypeptides with predictable chain lengths and low dispersities. We conducted structural work to examine their aqueous conformations and found that a high content of free OH Thr induces the formation of water-insoluble β-sheets. However, glycosylation appears to induce a polyproline II-type helical conformation, which sheds light on the role of glyco-Thr in rigid proteins such as mucins and collagen.

Influence of the block copolypeptide surfactant structure on the size of polypeptide nanoparticles obtained by mini emulsion polymerisation

Polypetide nanoparticles obtained by miniemulsion polymerisation of amino acid N-carboxyanhydrides (NCA) are a novel class of tuneable bio-derived functional nano materials for potential applications in nutraceutics, agriculture, and medicine. This...